1. Field of the Invention
The invention relates to a control device for an internal combustion engine and, more particularly, to a control device that has a function of detecting a fuel property.
2. Description of the Related Art
There are a variety of components of fuels for internal combustion engines, and internal combustion engines adapted to the use of a blended fuel, such as an alcohol-blended fuel obtained by blending ethanol, methanol or the like with gasoline, have been put into practical use. Therefore, it is desirable that the property of the fuel can be detected on the vehicle side.
For the purpose of detecting the fuel property on the vehicle side, a device disclosed in Japanese Patent Application Publication No. 2000-170581 (JP-A-2000-170581) corrects the air-fuel ratio if an engine start failure or the like is detected, and, from the air-fuel ratio correction amount, estimates a theoretical air-fuel ratio (stoichiometric air-fuel ratio), and estimates an octane number from the theoretical air-fuel ratio.
Besides, a device disclosed in Japanese Patent Application Publication No. 64-88153 (JP-A-64-88153) detects the fuel property by calculating the calorific value in the cylinders from the detected value of the in-cylinder pressure, and therefore finding the lower calorific value of the fuel.
Besides, a technology of Japanese Patent No. 2907594 includes a storage device that stores relationships between the alcohol concentration in fuel, the theoretical air-fuel ratio, and the light/heavy component ratio of gasoline, and detects the light/heavy component ratio of the gasoline by comparing the data on the detected alcohol concentration and the detected theoretical air-fuel ratio (stoichiometric air-fuel ratio) with the data stored in the storage device.
However, the device of Japanese Patent Application Publication No. 2000-170581 (JP-A-2000-170581) is not able to detect the fuel property unless an engine start failure is detected, and also requires a considerable amount of time in order to converge the air-fuel ratio to the stoichiometric air-fuel ratio. The device of Japanese Patent Application Publication No. 64-88153 (JP-A-64-88153) is not able to control the air-fuel ratio. As for the device of Japanese patent No. 2907594, the alcohol concentration and the stoichiometric air-fuel ratio need to be found by other devices or the like, so that a simpler device is desired. In the meantime, there is no known control device that utilizes a relationship between the calorific value and the stoichiometric air-fuel ratio.